1. Field of the Invention
The present invention relates to a dose monitor chamber for radiation. In particular, this invention relates to a dose monitor chamber for electrons or X-rays, preferably for use in or in conjunction with a linear accelerator.
2. Description of the Prior Art
U.S. Pat. No. 4,131,799 discloses a dose monitor chamber or ionization chamber which is employed to monitor the radiation exiting from a particle accelerator. Of interest is not only the totally emitted radiation intensity but also the (uniform or irregular) distribution of the radiation within the emitted radiation cone. The known monitor chamber detects all kinds of nonhomogeneities of the dose rate. In particular, it is applicable for determining asymmetries as well as changes of electron or X-ray distribution. The ionization chamber according to the prior art comprises essentially a first electrode arrangement in a first plane and a second electrode arrangement located in a second plane parallel to the first plane. The first arrangement contains a round central plate which functions as an electrode and which is surrounded by four further plates. These plates are insulated from each other and are symmetrically arranged with respect to the central plate. They also serve as electrodes. The ionization chamber further comprises a spacing ring for keeping the second arrangement of electrodes in a plane parallel to the first arrangement, thereby forming a first chamber. The second electrode arrangement is a round plate which is supplied by a high voltage. The current derived from the individual measuring electrodes is proportional to the dose rate received in the corresponding measuring volume. To the ionization chamber is connected a second chamber, where the totally received dose rate is measured.
In such a dose monitor chamber having a multi-electrode system the problem arises that a plurality of electric signals must be conducted out of the chamber(s) without electrical interference and then must be processed. This means that a comparatively large number of preamplifiers and of subsequent electronic components is necessary. Furthermore, cables and insulated boxes or openings for the electric wires are required in corresponding number. It is apparent that such a dose monitor chamber having a multi-electrode system is expensive and presents a complicated mechanical construction.